The invention relates to specific prepolymers especially useful as monomers that can be formed into biomedical devices.
Heretofore, biomedical materials especially useful commercially as contact lenses have been based upon polymers and/or copolymers of a select set of chemistries. Methylmethacrylic acid type chemistries form the oldest type, the polymers from which poly(methylmethacrylates) (PMMA) have been surpassed by hydrogel chemistries based upon poly(hydroxyethyl methacrylate) (pHEMA) or polyvinyl pyrrolidinone (pNVP), and copolymers of HEMA and NVP. These materials formed the basis for most soft contact lenses.
Silicone chemistries have played a lesser role in the marketplace, but have offered higher oxygen permeabilities than their hydrogel counterparts. They have, however, presented certain performance characteristics which limit their applicationxe2x80x94specifically surface wettability problems.
Copolymers employing PMMA types of chemistry have been employed in conjunction with silicone chemistry and hydrogel chemistry to produce a wide assortment of materials which have the common characteristics of high oxygen permeability and high modulus (rigidity). These materials have been characterized as hard gas permeable or rigid gas permeable materials.
Urethane chemistries have not been employed commercially in the contact lens market despite significant work in the area such as U.S. Pat. No. 3,786,034 issued to Blair et al relates to hard, hydrophilic polyurethane material formed from reacting a specific polyol with a polyfunctional isocyanate. U.S. Pat. No. 3,821,186 teaches similar materials as U.S. Pat. No. 3,786,034.
U.S. Pat. No. 4,136,250 teaches a polymer formed by reacting a high molecular weight polydimethyl siloxane diol with 2 mole equivalents isophorone diisocyanate and then reacting with excess hydroxy containing monomers. Essentially, this is a soft segment prepolymer endcapped with ethylenically reactive endcap. These materials are relatively weak and in their hydrated form show low degrees of elongation.
U.S. Pat. No. 4,309,526 teaches adhesive compositions which employ low molecular weight polyols reacted with diisocyanates and short chain cycloaliphatic or aromatic diols, endcapped with hydrophilic endcaps. Various characteristics such as oxygen permeability are not mentioned.
U.S. Pat. No. 4,359,553 teaches polyurethane diacrylate compositions useful as biomedical materials which are formed by reacting a diol mw 200 to 20,000 with 2 mole equivalents diisocyanate which is then reached with diethyleneglycol diacrylate to form the water soluble polyurethane. Specific applications taught in the patent are as controlled release matrices.
U.S. Pat. No. 4,454,309 teaches a hydrophilic random block copolymer with polyurethane linkage between randomly using high molecular weight polyols and low molecular weight ethylene mers. The materials absorbed 100-500% by weight additional water.
U.S. Pat. No. 4,740,533 teaches materials which are block copolymers of polyoxyalkylenes and polysiloxanes which have no hard segments.
U.S. Pat. No. 4,780,488 teaches a prepolymer with only a central soft segment endcapped with hydroxyethyl methacrylate endcaps or the like.
The art does not disclose polyurethane prepolymers useful as biomedical materials with the hard-soft-hard or the soft-hard-soft configurations disclosed herein which are oxygen permeable and still exhibit exemplary physical strength characteristics. Nor does the art teach that these prepolymers are useful as biomedical materials.
The present invention relates to prepolymers especially useful in biomedical copolymers of the general formula:
E(*D*A*D*G)a*D*A*D*Exe2x80x2
or 
E(*D*G*D*A)a*D*G*D*Exe2x80x2
where
A denotes a divalent polymeric radical chosen from the group of
"Parenopenst"CH2)nxe2x80x2xe2x80x94Oxe2x80x94(RPO)nxe2x80x94(CH2)nxe2x80x3xe2x80x94
"Parenopenst"CH2)mxe2x80x2xe2x80x94Oxe2x80x94(RFO)mxe2x80x94(CH2)mxe2x80x3xe2x80x94
wherein
RP denotes a straight or branched alkyl group with 1 to 6 carbon atoms and n provides for a moiety weight of the radical between 2000 and 10,000;
RF denotes a fluorinated straight or branched alkyl radical with 1 to 6 carbon atoms and m provides a moiety weight of between 400 and 10,000;
RS denotes an alkyl radical or a short chain fluorinated alkyl radical with 1 to 3 carbon atoms; and
p provides a moiety weight of 400 to 10,000;
D denotes an alkyl diradical, an alkyl cycloalkyl diradical, a cycloalkyl diradical, an alkylaryl diradical or an aryl diradical, with 6 to 30 carbon atoms;
G denotes an alkyl diradical, a cycloalkyl diradical, an alkyl cycloalkyl diradical, an aromatic diradical or an alkylaromatic diradical with 1 to 40 carbon atoms which may have ether, thio, or amine linkages in the main chain;
* denotes a urethane or ureido linkage; and
E and Exe2x80x2 denote polymerizable unsaturated organic radicals represented by the general chemical formula 
wherein
R1 denotes a divalent alkylene radical with 1 to 10 carbon atoms;
R2 denotes a xe2x80x94H or xe2x80x94CH3 radical;
R3 denotes a xe2x80x94H radical or an alkyl radical with 1 to 6 carbon atoms or a 
radical where
Y is xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94 and R4 denotes an alkyl radical with 1 to 12 carbon atoms; 
Ar denotes an aromatic radical with 6 to 30 carbon atoms;
a is at least 1;
w is 0 to 6;
x is 0 or 1;
y is 0 or 1; and
z is 0 or 1.
These prepolymers are especially useful in forming copolymerizates with ethylenically unsaturated monomers which are known and used in the biomedical materials field. The resultant copolymers have a combination of oxygen permeability, surface wettability and physical strength in dry and/or hydrated forms otherwise unavailable.
The prepolymers of the present invention are especially useful in making biomedical materials due to this combination of physical strength and high oxygen permeability when copolymerized with state of the art ethylenically unsaturated biomedical monomers. The combination of advantageous properties is achieved due to the specific chemistry inherent in the claimed prepolymer.
The prepolymers of the invention can be represented by the general formulae:
E(*D*A*D*G)a*D*A*D*Exe2x80x2
or 
E(*D*G*D*A)a*D*G*D*Exe2x80x2
where
A denotes a divalent polymeric radical chosen from the group of
"Parenopenst"CH2)nxe2x80x2xe2x80x94Oxe2x80x94(RPO)nxe2x80x94(CH2)nxe2x80x3xe2x80x94
"Parenopenst"CH2)mxe2x80x2xe2x80x94Oxe2x80x94(RFO)mxe2x80x94(CH2)mxe2x80x3xe2x80x94
wherein
RP denotes a straight or branched alkyl group with 1 to 6 carbon atoms and n provides for a moiety weight of the radical between 2000 and 10,000;
RF denotes a fluorinated straight or branched alkyl radical with 1 to 6 carbon atoms and m provides a moiety weight of between 400 and 10,000;
RS denotes an alkyl radical or a short chain fluorinated alkyl radical with 1 to 3 carbon atoms; and
p provides a moiety weight of 400 to 10,000;
D denotes an alkyl diradical, an alkyl cycloalkyl diradical, a cycloalkyl diradical, an alkylaryl diradical or an aryl diradical, with 6 to 30 carbon atoms;
G denotes an alkyl diradical, a cycloalkyl diradical, an alkyl cycloalkyl diradical, an aromatic diradical or an alkylaromatic diradical with 1 to 40 carbon atoms which may have ether, thio, or amine linkages in the main chain;
* denotes a urethane or ureido linkage; and
E and Exe2x80x2 denote polymerizable unsaturated organic radicals represented by the general chemical formula 
wherein
R1 denotes a divalent alkylene radical with 1 to 10 carbon atoms;
R2 denotes a xe2x80x94H or xe2x80x94CH3 radical;
R3 denotes a xe2x80x94H radical or an alkyl radical with 1 to 6 carbon atoms or a 
radical where
Y is xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94NHxe2x80x94 and R4 denotes an alkyl radical with 1 to 12 carbon atoms; 
Ar denotes an aromatic radical with 6 to 30 carbon atoms;
a is at least 1;
w is 0 to 6;
x is 0 or 1;
y is 0 or 1; and
z is 0 or 1.
The prepolymers upon polymerization form two domains which can be characterized as hard and soft domains, respectively. The soft domain generally have glass transition temperatures (Tg s) lower than room temperature whereas the hard domains have Tg s higher than room temperature. Upon polymerization, the hard segments of the prepolymer associate with one another and the soft segments form the soft domain which account for the oxygen permeability of the polymeric mass. The combination of hard and soft segments provides the polymer with superior mechanical properties otherwise unavailable.
The hard segments of the prepolymer are formed by the reaction of the short chain diol with the diisocyanate. Thus, in the formulae supra, the xe2x80x9chard segmentsxe2x80x9d are represented by the *D*G*D* portions of the formulae. Thus termed, formula (i) represents a hard-soft-hard prepolymer and formula (ii) represents a soft-hard-soft prepolymer.
The isocyanates which can be used in preparation of the invention include, toluene diisocyanate, 4,4xe2x80x2-diphenyl diisocyanate, 4,4xe2x80x2-diphenylene methane diisocyanate, p-phenylene diisocyanate, dianisidine diisocyanate, 1,5 napthalene diisocyanate, 4,4xe2x80x2-diphenyl ether diisocyanate, 4,4xe2x80x2(dicyclohexyl)methane diisocyanate, 1,3-bis-(isocyanato methyl)cyclohexane, cyclohexane diisocyanato, tetrachlorophenylene diisocyanate, isophorone diisocyanate, and 3,5-diethyl-4,4xe2x80x2-diisocyanato diphenyl methane.
Other diisocyanates which may be used are higher molecular weight diisocyanate formed by reacting polyamines which are terminally capped with primary or secondary amines, or polyhydric alcohols with excess of any of the above described diisocyanates. In general, these high molecular weight diisocyanates will have the general formula 
wherein R is a divalent organic radical with 2 to about 20 carbon atoms, X is xe2x80x94Oxe2x80x94, or xe2x80x94NRxe2x80x2xe2x80x94, where R is xe2x80x94H or a lower alkyl, and B is a divalent organic radical.
The diisocyanate is reacted with low molecular weight diols or glycols such as 2,2-(4,4xe2x80x2dihydroxydiphenyl)-propane (bisphenol-A), 4,4xe2x80x2-iso-propylidine dicyclohexanol (hydrogenated biphenol-A), ethoxylated bisphenol-A, propoxylated bisphenol-A, 2,2-(4,4xe2x80x2-dihydroxydiphenyl)-pentane, xcex1,xcex1-(4,4xe2x80x2-dihydroxydiphenyl)-p-diisopropyl benzene, 1,3 cyclohexane diol, 1,4-cyclohexane diol-1,4-cyclohexane dimethanol, bicyclic and tricyclic diols such as 4,8-bis-(hydroxymethyl)-tricyclo[5.2.1.02,6]decane, neopentyl glycol, 1,4 butanediol, 1,3-propanediol, 1,5-pentanediol, diethylene glycol, triethylene glycol and the like.
These hard segments as mentioned before form hard domains in the final polymer or copolymer by association via hydrogen bonding with other rigid segments. The degree of association within the hard domain can be modified by controlling the amount of hydrogen bonding between the segments by either 1) decreasing the overall weight content of the hard segment in the prepolymer by increasing the molecular weight of the soft segment or 2) by decreasing the amount of hydrogen bonding density in the hard segment by either using relatively soft, longer chained diols, or by using primary amines or secondary amines capped low molecular weight compounds in conjunction with the diisocyanates rather than the diols.
The hard segments are then reacted with a relatively high molecular weight polymer which is xcex1,xcfx89-endcapped with two active hydrogens, usually hydroxyl groups. These segments form the so-called soft segment of the prepolymer. Various types of high molecular weight polymers can be used including in general polymers of the following formulae
a) HO(CH2)(RPO)n(CH2)OH;
b) HO(CH2)(RPO)m(CH2)OH; and 
Formulae a) represents polyoxyalkyleneglycols which are generally commercially available in the molecular weight range called for in the present invention. These diols include polymers prepared from the epoxides: ethylene oxide 1,2-propylene oxide, 1,2-butylene oxide, 2,2 epoxydecane, 1,2-epoxyoctane, 2,3-epoxy norborane, 1,2-epoxy-3-ethoxy propane, 2,2-epoxy-3-phenoxypropane, 2,3-epoxypropyl-4-methoxy phenyl ether, tetrahydrofluran, 1,2-epoxy-3-cyclohexyloxy propane, oxetane, 1,2-epoxy-5-hexene, 1,2-epoxyethylbenzene, 1,2-epoxy-1-methoxy-2-methylpropane, benzyloxy propylene oxide, the like and combinations thereof.
The preferred polymers of this class are polypropylene glycols of molecular weights, 2000, 3000 and 4000 and more and polyoxyethylene polyoxypropylene block copolymers with molecular weight greater than 2000.
Formulae b) represents polyfluoroethers with xcex1,xcfx89-active hydrogens. This class of polymers can be synthesized per the heading of U.S. Pat. No. 3,810,874. Generally, these polymers should have molecular weights between 400 and 10,000 to be useful in the present invention.
Formulae c) represents a xcex1,xcfx89-dihydroxyl alkyl endblocked polysiloxane which for the purpose of the present invention should have a molecular weight in the range of 400 to 10,000. These polysiloxanes can be synthesized by reacting a disiloxane of the general formula 
with cyclopolydimethyl siloxane under acidic conditions.
Alternately, the disiloxane can be replaced with dimethoxydimethylsilane or diethoxy dimethyl silane to produce the xcex1,xcfx89-dihydroxy endcapped polysiloxanes.
The endcapping monomers used in the prepolymer are generally represented by the formula 
as defined supra. The Stage B reaction product is reacted with an excess of suitable acrylate or methacrylate esters containing a hydroxy or amine group on the non-acrylate or non-methacrylate portion of the monomer to form the endcaps of the above formula. Suitable endcap monomers include hydroxyethyl acrylate, hydroxyethyl methacrylate, aminoethyl methacrylate, 3 hydroxypropyl methacrylate, amino propyl methacrylate, hydroxyhexylacrylate, t-butylaminoethyl methacrylate, monoacrylate or monomethacrylate esters of bisphenol-A and/or bisphenol-B.
The prepolymers of the present invention are formed by two general synthetic approaches. One approach produces the hard-soft-hard prepolymer while the second approach produces the soft-hard-soft prepolymer. Variations of each scheme were found to be necessary for specific rigid/soft segment combinations, details of which are disclosed in the examples.
The scheme used to produce this type of prepolymer employed three stages to produce the final prepolymer. The first stage (STAGE A) involved reacting 2 mole equivalents of diisocyanate with about 1 mole equivalent low molecular weight diols described herein. If these diols could be represented by the symbol ▴G▴, where ▴ denotes a hydroxyl radical and G represents the rest of the diol compound, and the diisocyanate functional compound could be represented by xe2x97xafDxe2x97xaf where xe2x97xaf represents an isocyanate radical, the STAGE A reaction can be schematically represented as follows:
2xe2x97xafDxe2x97xaf+▴G▴xe2x86x92xe2x97xafD*G*Dxe2x97xaf
where * denotes a urethane or a ureido linkage. STAGE A produces a so-called xe2x80x9cHardxe2x80x9d segment. As is known to those skilled in polymer chemistry, the product xe2x97xafD*G*Dxe2x97xaf is the mathematical average of all reaction product molecules. The reaction product of the actual reaction will contain xe2x97xaf◯xe2x97xaf and xe2x97xafD(*G*D)c*G*D with cxe2x89xa72. Again, the formulas are numerical averages.
STAGE B involves reacting about one half mole equivalent of a xcex1,xcfx89-diol endcapped long chain polymer with the reaction product of STAGE A. If ▴A▴ represents the long chain diol the STAGE B Reaction is
2xe2x97xafD*G*Dxe2x97xaf+▴A▴xe2x86x92[xe2x97xafD*G*D*]2A 
In STAGE C, the reaction product from STAGE B is reached with a molar excess of an endcapping monomer which has: 1) hydroxyl or amine functionality; and 2) some polymerizable unsaturation. If the endcapper is represented by the symbol E▴, where is xe2x80x94OH or xe2x80x94NH2 or xe2x80x94NHxe2x80x94, the reaction proceeds generally as
[xe2x97xafD*G*D*]2A+2E▴xe2x86x92[E*D*G*D*]2A 
Optionally, STAGE B can be run with molar excess of A to produce multiblock polymers of the general formula xe2x97xaf(D*G*D*A)a*D*G*Dxe2x97xaf where a is at least 1. This reaction product would be endcapped in STAGE C above.
The second general synthetic scheme using the same nomenclature described is represented by the following general formulae:
2xe2x97xafDxe2x97xaf+▴A▴xe2x86x92[xe2x97xafD*]2A 
2[D*]2A+▴G▴xe2x86x92[xe2x97xafD*A*D*]2G 
[xe2x97xafD*A*D*]2G+2E▴xe2x86x92[E*D*A*D*]2G 
In general, each of the reaction stages is run until the reactive step is complete. Reaction progress in STAGES A and B reactants were monitored by acid base titration. The isocyanate content was calculated by the difference of acid equivalents between a stock solution dibutylamine and its reaction product with the diisocyanate reaction intermediate. The reaction was also monitored by ATR-IR for the appearance/disappearance of peaks at 1700 cmxe2x88x921, which indicated the presence of 
and 2250 cmxe2x88x921 which indicated consumption of xe2x80x94Nxe2x95x90Cxe2x95x90O.
It was found that the synthesis of the prepolymer could be run neat or in solution. A wide range of aprotic solvents can be used to synthesize the prepolymers of the present invention. Solvents useful in the synthesis include toluene, methylene, chloride, benzene, cyclohexane, hexane, heptane and the like. Preferred solvents are toluene, methylene chloride and mixtures thereof.
Reaction of the prepolymer precursors may be accomplished in the presence or absence of catalysts for urethane reactions, such catalysts being well known in the art. The first step of prepolymer synthesis where diisocyanate is first reacted with a short carbon chain (2 to 30 carbon atoms) diol, particularly where an aromatic diisocyanate is used, proceeds very rapidly, even in the absence of any catalyst. In fact, during the step of reacting diisocyanate and short chain diol, temperature control may be required in order to avoid/minimize side reactions.
Preferably, the first step of prepolymer synthesis in accordance with the present invention is carried out below about 100xc2x0 C., most suitably within the range of from about 60xc2x0 C. to about 90xc2x0 C. Thereafter, the second step of the reaction is carried out at comparable temperatures, preferably within the range of from about 40xc2x0 C. to 70xc2x0 C. The final step of prepolymer formation suitably is effected at temperatures of from about room temperature to about 100xc2x0 C., with a narrow range of from about 40xc2x0 C. to about 50xc2x0 C. being most preferred. As will be apparent to those skilled in the art, optimal reaction conditions, such as temperatures and duration, are selected for each individual reaction system to achieve conditions that produce a favorable rate of reaction without fostering undesirable side reactions.
Among the suitable catalysts for use in prepolymer formation are tin salts and organic tin esters, such as dibutyl tin dilaurate, tertiary amines, such as triethyl diamine and other recognized catalysts, such as 1,4-diaza (2.2.2)-bicyclooctane (DABCO).
The prepolymers of the present invention are particularly useful as comonomers with state of the art ethylenically reactive monomers useful in the field of biomedical materials. In general, these monomers are the hydroxyalkyl acrylates and diacrylates such as hydroxyethyl acrylate, hydroxypropyl acrylate, and the corresponding methacrylate compounds, including cyclohexyl methacrylate, methyl methacrylate, isobornyl methacrylate, lauryl methacrylate, triethylene glycol dimethacrylate, isobuty methacrylate and tetrahydrofurfuryl methacrylate and other unsaturated reactive monomers such as acrylamides, methacrylamides, pyrrolidinones, stryene and acrylonitrile can be used as well and other monomers known in the art including fluorinated analogs of all of the previously mentioned monomers and the organo silicone comonomers known in the art. Specific fluorocomonomers include:
(2,2,2-trifluoroethyl) itaconate
(hexafluoroisopropyl) itaconate
(1H, 1H-perfluorooctyl) itaconate
(1H, 1H, 111H-perfluoroundecyl) itaconate
(perfluoro-t butyl) itaconate
(pentafluorophenyl) itaconate
(2H, 2H-perfluorobenzyl) itaconate
(pentafluorophenylmethyl) itaconate
(decafluorocyclohexyl) itaconate
(1H-perfluorocyclohexyl) methyl itaconate
(1,1,1-trifluoroisopropyl) itaconate
1-methyl-4-(hexafluoroisopropyl) monoitaconate
4-(hexafluoroisopropyl) monoitaconate
1-(1H, 1H-perfluorooctyl)-4-hexafluoroisopropyl) itaconate
and methacrylate analogs thereof.
Specific organosilicon comonomers include:
tris(2-acetoxyethyldimethylsiloxy)silylpropyl acrylate and methacrylate
tris(2-carboxyethyldimethylsiloxy)silylpropyl acrylate and methacrylate
tris(3-hydroxypropyldimethylsiloxy)silylpropyl acrylate and methacrylate
acrylate and methacrylate functional, fluorosubstituted alkyl/aryl siloxanes such as:
tris(3,3,3 trifluoropropyl dimethylsiloxy) silyl propyl acrylate and methacrylate
tris[3-heptafluoroisopropoxy propyl)] dimethysiloxy silylpropyl acrylate and methacrylate
tris(pentafluorophenyl dimethysiloxy)silyl propyl acrylate and methacrylate
Other potentially useful organosilicon comonomers include:
p-(pentamethyldisiloxanyl) styrene
bis(trimethylsiloxy)
pyrrolidinonyldimethyl
siloxy-silylpropyl acrylate and methacrylate.
When used as comonomers these materials can be used from 5 to 85 weight percent of the final copolymer weight with the balance comprising the prepolymer portion.
Other di-ethylenically reactive monomers can also be used to effect the mechanical and surface properties. Such crosslinks are generally employed in the 0.1 to 5 wt % range.
The polymers and copolymers are formed by a free radical mechanism using a wide variety of known free radical catalysts such as the diacyl peroxides such as benzoyl peroxide; dialkyl peroxides such as di-tert, -butyl peroxide; ketone peroxides such as methylethyl ketone peroxide; and peresters which readily hydrolyze, e.g. tert-butyl peracetate, tert-butyl perbenzoate, di-tert-butyl diperphthalate, etc. A particularly useful class of peroxy initiators are the organic hydroperoxides such as cumene hydroperoxide, methylethyl ketone hydroperoxide, tert-butyl hydroperoxide, etc. The initiators should be used at a concentration of about 0.01 percent to about 10 percent by weight of the total formulation, preferably about 0.1 percent to about 5 percent by weight. Another useful class of initiators comprises carbonyl-containing ultraviolet-activated free radical generators, such as acetophenone, benzophenone, and the benzoin ethers. Other suitable UV initiators are known in the art. Initiator mixtures may also be used.
Solvents can be used in the final copolymerization and/or polymerization process. Solvent choice will depend upon the solubility parameters of the prepolymer and of the comonomers used, if any, and should be chosen to allow full solubilization of all polymerizate components.
In certain instances, the copolymerization process should be carried out without solvent. For instance, when 2-hydroxyethyl methacrylate (HEMA) is copolymerized with one of the prepolymers formed with polyethylene glycol, use of toluene causes the HEMA to form heterogenous domains which are not stable under aggressive hydrolytic conditions.
Some of the preferred copolymers are polymerized from the following comonomer mixtures:
Various homopolymers and copolymers films were formed and characterized by standard testing procedures such as:
1. Tensile strength (g/mm2) and modulus of elasticity were measured per ASTM test method D1708.
2. Elongation was measured per ASTM 1708.
3. Initial tear strength and propagation tear strength were measured per ASTM 1438.
4. Oxygen permeabilities were measured by the method reported by Relojo, M. et al in Contact and Intraocular Lens Medical Journal, Vol. 3, issued p. 27 (1977) and edge effects were accounted for per the methods described by Fatt, et al. in International Contact Lens Clinic, V. 14, p. 389 (1987).
5. Water content is measured per a gravimetric method.
6. Refractive index was measured per typical methods on hydrated samples using a refractometer.
As mentioned, the prepolymers of the present invention are particularly useful in forming shaped articles used in biomedical applications. These polymers and copolymers can be used to make biomedical devices i.e. shaped articles, such as dialyzer diaphragms, to prepare artificial kidneys and other biomedical implants, such as disclosed in Wichterle, U.S. Pat. No. 2,976,576 and Wichterle, U.S. Pat. No. 3,220,960. The instant polymers and copolymers can be used in preparing therapeutic bandages as disclosed in Shephard, U.S. Pat. No. 3,428,043. The instant polymers and copolymers can also be used in preparing medical surgical devices e.g. heart valves, vessel substitutes, intra-uterine devices, membranes and other films, dialyzer diaphragms, catheters, mouth guards, denture liners and other such devices as disclosed in Shephard U.S. Pat. No. 3,520,949 and Shephard U.S. Pat. No. 3,618,231. The instant polymers and copolymers can be used to modify collagen to make blood vessels, urinary bladders and other such devices as disclosed in Kliment U.S. Pat No. 3,563,925. The instant polymers and copolymers can be used to make catheters as disclosed in Shephard U.S. Pat. No. 3,566,874. The instant polymers and copolymers can be used as semipermeable sheets for dialysis, artificial dentures and all of such disclosures as set forth in Stoy U.S. Pat. No. 3,607,848. The instant polymers and copolymers can be used in ophthalmic prostheses and all other uses disclosed in Wichterle U.S. Pt. No. 3,679,504. They may also be used as a polymeric matrix for controlled release of active pharmaceutical agents.
In the following examples, the properties of such films derived from the claimed prepolymer and combinations of prepolymers with various comonomers are described. For certain comonomers which employed xe2x80x9chydrophilicxe2x80x9d comonomers, the films were hydrated to xe2x80x9chydrogelxe2x80x9d states their physical properties were measured as hydrated. The following examples are meant to illustrate the invention, but do not define the final scope of the invention.